The invention relates to a discontinuous centrifuge comprising a rotatable centrifuge drum incorporating a drive spindle, a casing and a base, a hub of the centrifuge drum which hub has a plurality of arms for the indirect or direct connection of the casing of the centrifuge drum to the drive spindle of the centrifuge drum, a scraper for scraping a product off the inner wall of the casing of the rotatable centrifuge drum at a scraper rotational speed, wherein the scraper comprises an element which is pivotal about an axis, which axis extends in parallel with the axis of rotation of the centrifuge drum, wherein the element comprises a blade which extends over almost the entire height of the centrifuge drum and makes contact with the product after the pivotal movement.
Discontinuous centrifuges are also used especially for the separation of sugar crystals from sugar crystal suspensions.
A starting material, a magma with enriched crystal suspensions for example, is supplied from above and is then treated in the centrifuge drum in such a way that a product, here for example a crystallised mass, is deposited on the inner surface of a casing of the centrifuge drum. The syrup passes out through a working filter which is located on the casing.
This crystallised mass or these crystal layers then have to be scraped out of the centrifuge drum so that it is ready for the next input or the next charge.
From DE 36 14 965 A1, there is known a centrifuge drum for a discontinuously operating flat bottom centrifuge. The drum base is fastened to a drum casing. The flat bottom of the drum falls away partially towards the hub of the centrifuge in order to enable the crystallised mass to discharge through openings in the base.
A discontinuous centrifuge such as the one described in EP 0 953 380 B1 has proved to be very well-suited for the scraping process. The crystal layers are removed from the inner surface of the casing of the centrifuge drum by means of a scraper which extends over the entire height of the centrifuge drum and can be swung about an axis parallel to the centrifuge drum in such a way that a blade thereof enters the sugar layers (or layers of another product) on the inner surface of the casing and gradually peels the crystallised mass off the casing in this way.
The crystal layers that have been peeled in this way then fall downwardly within the centrifuge drum onto the base thereof due to the force of gravity and are then removed therefrom through a central opening therein.
It should be taken into consideration thereby that in the lower region of the centrifuge drum there is a hub having a plurality of arms which connects the casing of the centrifuge via the base to a shaft or drive spindle which provides the drive means for the rotation of the centrifuge drum and runs in the axle of the centrifuge drum.
In order to enable the substantial forces to be transferred from this spindle to the centrifuge drum rotating at high-speed or via the base to the casing, this hub is reinforced and strengthened three-dimensionally by means of built-in features, inclined arms and further elements.
Since the scraper and the blade or peeling knife thereof and the elements of the hub and the arms thereof would mutually interfere, the scraper is moved upwardly parallel to the axis by about 200 mm during the centrifuging process.
Before the peeling process, the scraper then travels vertically or parallel to the axis back towards the bottom of the centrifuge drum to its lowest point and it is only then that it is pivoted about the pivotal axis into the sugar layers.
From DE 10 2009 039 729 A1, there is known a centrifuge for a completely different purpose. There, a shaver/knife device is proposed as a scraper for a centrifuge that is mounted in pendulum-like manner for the purposes of stripping-off caked-on material. A plurality of shavers are mounted on an arm which extends in parallel with the shaft of the centrifuge drum and engage in knives that protrude from the cylinder wall. Moreover, an inner housing is provided. The entire conception is not suitable for sugar centrifuges.
From BR-MU 8800278-0 U, a proposal is known for additionally safeguarding this vertical travel of a scraper by means of a locking device so as to ensure that the pivotal process will only occur when the scraper is in the correct position. Moreover, it is also proposed that the length of the lowering stroke should be as small as possible.
Such an additional locking device increases the overall expenditure by quite a considerable amount. Apart from the additional costs, there is also the corresponding factor of the time that is necessary for the locking process and also for the process of unlocking this locking device in due course. Moreover, it relates to a device under load which entails additional wear and tear and also the danger of malfunctioning.
In a further proposal for a discontinuous centrifuge of this type that is known from EP 1 954 397 B1, it is proposed that two separate spade-like scrapers located one above the other be used rather than one scraper spanning the entire length of the centrifuge drum in the axial direction. In addition, the two partial scrapers are to be displaced from one another and should respectively scrape off an upper and a lower part of the centrifuge drum in a very complicated manner relative to each other. At the same time, the vertical stroke in the axial direction of the centrifuge drum for the two spade-like scrapers should be independently controllable and should also be restricted.
This conception is extraordinarily costly and requires an extremely complex arrangement in order to ensure the separate movement and control of the two spade-like scrapers.
The users of such discontinuous centrifuges are however interested in an operational mode of the centrifuge drum which is as smooth as possible and is least prone to errors. The layout on equipment should be as low as possible and the number of relatively moving parts as few as possible.
Moreover, it would be desirable if there were to be as little loss of time as possible from the real working time due to ineffective safeguards and the like.
Consequently, the object of the invention is to propose a discontinuous centrifuge which is capable of carrying out a scraping process on the inner wall of a casing of a centrifuge drum with reduced layout on equipment.